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On Friday 09 June 2006 22:45, Vladimir G. Ivanovic wrote: |
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> On Fri, 2006-06-09 at 20:50 +0200, Hemmann, Volker Armin wrote: |
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> > > If -ffast-math is filtered or stripped out, there is no harm in leaving |
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> > > it in CFLAGS, right? |
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> > |
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> > no, because a lot of other flags are filtered too! |
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> |
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> What??? Whether only -ffast-math is filtered or all flags are filtered, |
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> -ffast-math still filtered. I don't see where the harm lies. |
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the harm lies in an app, that does not filter and breaks in subtle ways when |
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compiled with fast-math. |
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> > |
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> > FOR SPECIAL APPS. AND THIS DOCUMENT IS MEANT FOR PROGRAMMERS! PEOPLE WHO |
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> > KNOW THEIR CODE! |
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> |
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> I didn't see anywhere that the AMD document is for special applications |
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> only. Where does it say that? |
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> |
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> What it does say is that applications the rely on exact implementation |
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> of IEEE rules or specifications for floating-point behavior shouldn't |
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> use -ffast-math. |
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again, that guide is for programmers, to optimze the code they wrote and they |
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know in and out. Not end users, who turn on every flag because it sounds |
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good. |
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> |
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> |
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> Chapter 1 Introduction, Section 1.1 Audience says: |
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> |
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> This document is intended for ISVs and end-users of the AMD |
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> Athlon 64 processor-based platforms... |
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> |
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> It's clear that you think using -ffast-math is dangerous. I don't, so I |
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> plan on continuing to use it. So far, the evidence from my system is in |
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> my favor. (I did run across two more instances, just today, where, in |
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> addition, to busybox, ebuilds fail with -ffast-math: cdparanoia and |
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> pcmciautils.) |
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I don't even think so, I know it. |
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I have seen enough people breaking their systems with ffast-math and similar |
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dangerous flags. |
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> |
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> What would make me change my mind is some evidence, or some authority |
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> who could convincingly explain why the experiences of those who do use |
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> -ffast-math is anomalous. SHOUTING OR MERELY ASSERTING THAT IT'S A |
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> PROBLEM is not really convincing. |
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maybe man gcc is evidence enough? |
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-- |
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